[GT87Stang]

I was just wondering if Flow numbers are everything when looking at heads? What else is there to look at?

[Brian@PAR]

No flow numbers are not everything. They are a rough comparison between heads but you do have to take them with a grain of salt.

Average cross section is something to look at and will help determine the heads capabilities.

Short side width as a function of valve size is important.

Valve to chamber cleareance is important.

Minimum cross section is important.

The valve job is important.

The big problem with heads is the really important stuff you won't know until you buy (then it's too late) or have independent reports on.

Some things like average cross section you can calculate just form the port volumes. The rest of it you can't so it can be a tough thing.

There are no shortage of people that are in love with one head or another. They'll say xxx head worked great for me but what does that really mean?

Here are some of the differences at least from a design standpoint.

TW heads are a cool design but the older base castings have some significant flaws such as tight chamber to valve cleareance and a small short side width. The latter is why the flow falls off over.550. They have plenty of meat for porting though so that is all fixed from reputable sources such as TEA. TFS has changed the casting over time to address some of these issues. Thier new FAST as CAST is supposedly a very nice head but I've not seen any independant testing on it yet.

Most other inline heads are pretty much the same so flow numbers can be a decent comparison but I would not spend an extra 500 on a set of heads that claim to flow 15 CFM more than another.

You then have the inline "modified" heads. High ports, Canfield and Ford Z304 heads all use a revised valve placement and valve angle (certain models). They are still an inline but the intake is roled towards the center to reduce shrouding and the exhaust ports are raised to improve flow. This can cause header issues when using high ports and the Z head. Also they use a special exhaust flange so headers are pricy. Canfields exhaust port is not raised nearly as much and most folks have no problems using standard headers. They also use the standard or the wide exhaust bolt pattern which is nice with big tube headers.

The RHS is a a bit of a mix. They moved the intake valve slightly but are a standard inline head. They have the dual bolt pattern exhaust but standard port location.

One more thing to consider after all of this is the hardware and springs you get with the head. Springs good for xxx lift, or "high rev" springs mean nothing. This is why we do not sell the "assembled" RHS head you'll find at other retailers. We use 10 degree locks and springs, valves, and rocker studs set up for the cam you're running in a one price head (1395 AL).

Now for your average street strip combo knowing the average cross section, the advertised flow (look at numbers above .500 closely), the head design and what parts you will be getting with the head is a good way to whittle the field. After that it is trusting the supplier and /or getting examples of real results on combo's that are similar to yours.

[e3sean]

Originally Posted by Brian@PAR No flow numbers are not everything. They are a rough comparison between heads but you do have to take them with a grain of salt. Average cross section is something to look at and will help determine the heads capabilities. Short side width as a function of valve size is important. Valve to chamber cleareance is important. Minimum cross section is important. The valve job is important. The big problem with heads is the really important stuff you won't know until you buy (then it's too late) or have independent reports on. Some things like average cross section you can calculate just form the port volumes. The rest of it you can't so it can be a tough thing. There are no shortage of people that are in love with one head or another. They'll say xxx head worked great for me but what does that really mean? Here are some of the differences at least from a design standpoint. TW heads are a cool design but the older base castings have some significant flaws such as tight chamber to valve cleareance and a small short side width. The latter is why the flow falls off over.550. They have plenty of meat for porting though so that is all fixed from reputable sources such as TEA. TFS has changed the casting over time to address some of these issues. Thier new FAST as CAST is supposedly a very nice head but I've not seen any independant testing on it yet. Most other inline heads are pretty much the same so flow numbers can be a decent comparison but I would not spend an extra 500 on a set of heads that claim to flow 15 CFM more than another. You then have the inline "modified" heads. High ports, Canfield and Ford Z304 heads all use a revised valve placement and valve angle (certain models). They are still an inline but the intake is roled towards the center to reduce shrouding and the exhaust ports are raised to improve flow. This can cause header issues when using high ports and the Z head. Also they use a special exhaust flange so headers are pricy. Canfields exhaust port is not raised nearly as much and most folks have no problems using standard headers. They also use the standard or the wide exhaust bolt pattern which is nice with big tube headers. The RHS is a a bit of a mix. They moved the intake valve slightly but are a standard inline head. They have the dual bolt pattern exhaust but standard port location. One more thing to consider after all of this is the hardware and springs you get with the head. Springs good for xxx lift, or "high rev" springs mean nothing. This is why we do not sell the "assembled" RHS head you'll find at other retailers. We use 10 degree locks and springs, valves, and rocker studs set up for the cam you're running in a one price head (1395 AL). Now for your average street strip combo knowing the average cross section, the advertised flow (look at numbers above .500 closely), the head design and what parts you will be getting with the head is a good way to whittle the field. After that it is trusting the supplier and /or getting examples of real results on combo's that are similar to yours.

hey man you seem to know your shit when it comes to heads. what is PAR all about and where in phoenix are you? there are a bunch of phoenix guys here.

[93mustank]

Heres your answer..looks like they custom grind......do you guys just submit to comp cam for these custom cams?

[Nitrous Injected]

what is cross section?
valve to chamber clearence?
small short side width?
Pease help with the termanoligy....i am a spung and i love to learn

[93hatch]

Originally Posted by e3sean hey man you seem to know your shit when it comes to heads. what is PAR all about and where in phoenix are you? there are a bunch of phoenix guys here.

i asked the same thing in a diff thread and dont think he ever replied

[Brian@PAR]

Sorry if I missed a reply to your thread. Sometimes they get lost in the mix.

Ok Pete Anderson Racing. We are a new start up and sell via the web. A good friend of mine and I decided to start selling parts instead of just building motors for our buddies. We have a deal with a group that allows us to sell all of the COMP performance brands as well as Canfield and Trickflow heads. The RHS stuff is where most of our focus is at mainly to give this head more exposure. It's a good piece and the price is right especially for what you get. We build each set as they are ordered so the customer gets the right part not something close. There is no up charging for solid roller cams even though this usually requires longer valves and more expensive spring.

The custom cams are not just a COMP lobe that we order. We have a deal with a grinder and each cam is designed then ground from a blank core and and cam doctored.

I'm not here to sell parts. I'm here to share what I know and maybe help guys spend their money wisely. If I sell some parts along the way then that's great. I'm by no means a guru but I do pay attention when the gurus talk and like to share what I've learned

Now that the intro is out of the way.

Average Cross section is the average area of the port. You calculate it based on the runner volume, ie. 200 cc's, and the runner length. In the Ford world you have three lengths. TW which is 4.75, standard which is 5" and the Highport, Canfield and Z304 which is 5.25". Here is the formula:

runner cc/ 16.39 = x cubic inches, x/runner length= average cross section in square inches.

Valve to chamber clearance is the distance between the valve and the chamber wall when the valve valve is opened to the point where the center of the valve is even with the deck. This should be .400 or better.



Short side width is the width of the runner down at the valve. This is typically measured at the widest point and just below the seat. Typically it's up around the valve guide as shown here.



This should be 100% or more of the valve size to slow the charge down and help it make the turn into the cylinder. Depending on the head this can sometimes be fixed by porting. This and the clearance spec shows there is more to putting in bigger valves than a valve job.

These pictures were taken on a set of RHS215 heads which have none of these problems OOTB. The 215 even uses a 2.08 intake valve and maintains over 100% short side width and .400 clearance.

Another factor is minimum cross section. This is typically in the PR pinch area and is a direct measurement of the port *.95 to account for the corner radii.

You use CID and RPM to determine the minimum cross section to obtain peak HP at that rpm. Or if you know the MCSA you use that and CID to see where the head will "typically" make peak power.

All of these things are just measurements. How the head will flow will depend on a lot of things that I'm just not smart enough or experienced enough to be able to get in there with a grinder port. I look at OOTB measurements and design then if I think I need or want more I employ a trusted and experienced porter. Lots of guys say they port and polish (what the heck is polish anyway... It's like a 3/4 race cam it really means nothing) but I've seen many porters that just make things worse.

Again a lot of these things you won't know until you have already bought the heads. You can use some of the info you get for comparison on potential but the manufacturers leave out the important stuff and that's where it comes down to experience, independent testing/evaluation (magazines are a joke) or trusting someone who can explain why they say one head is better than another.

Ok well sorry for the book but I tend to go on. Now I'm going on to bed.